The humanistic culture paid special attention to the study of history and particularly to those periods that had so far been ignored or less known: among these the late Roman Empire and the Early Middle Ages, whose events were better focused above all thanks to a more diffused knowledge of the Greek. Such a knowledge allowed to directly access to Byzantine historiographers’ sources which were hardly known in the Latin West. An author of relevant importance to reconstruct the history of Europe in the Late Antiquity is Procopius of Caesarea who lived between the end of the fifth and the sixth century. Procopius’ narration is used indeed by Leonardo Bruni to illustrate his contemporaries on the events dealing with the war against the Goths and Italy’s annexation to the Eastern Empire. Bruni’s history, drawn out in 1441, had a remarkable success. As a matter of fact this work is transmitted by plenty of witnesses, among which the Canon. Misc. 551, a manuscript that had certainly belonged to Guarnerio d'Artegna’s collection, an evidence thereof being the littera antiqua script of Giovanni Belgrado, one of Guarnerio’s trustworthy collaborators, as well as the ornamentation assignable to the «same taste line and the same quality level» of other Guarnerio’s codices. Moreover, on the ms. there are notations of remarkable interest that are referable to Guarnerio’s milieu, too. In Guanerio’s inventory of 1461 the codex now kept in Oxford can be identified in the item nr 86: «Leonardus Aretinus de bello Gothorum in pergamenis deauratus»; since it was no longer recorded in the inventory drawn out in 1528 by Domenico Rangan, it can be inferred that the dispersion of the collection original core had occurred before that date.